An engine cylinder may be deactivated by ceasing combustion in the engine cylinder. Combustion in the cylinder may be ceased by stopping fuel from entering the cylinder. Further, if the engine is a spark ignited engine, spark supplied to deactivated cylinders may also be ceased. If intake valves and exhaust valves of deactivated cylinders continue to operate while combustion is ceased in deactivated cylinders, oxygen may be pumped from the engine intake manifold to an exhaust gas after treatment system. Performance of the exhaust gas after treatment system may degrade if excess oxygen is pumped to the exhaust gas after treatment system. Therefore, it may be desirable to stop air flow through deactivated cylinders while the engine continues to rotate. One way to stop air flow through deactivated engine cylinders is to hold intake and exhaust valves of deactivated cylinders in closed positions while the engine continues to rotate. However, cost of manufacturing such an engine may be prohibitive if all engine cylinders may be deactivated in this way.
The inventors herein have recognized the above-mentioned issues and have developed an engine method, comprising: holding exhaust valves of a cylinder of an engine closed and operating intake valves of the cylinder while rotating the engine through an engine cycle; and advancing intake valve timing of the cylinder at an engine speed and torque beyond a base intake valve timing of the cylinder at the engine speed and torque while rotating the engine through the engine cycle.
By holding exhaust valves closed and operating intake valves while an engine rotates, it may be possible to provide the technical result of selectively deactivate one or more cylinders of the engine without pumping oxygen to an exhaust gas after treatment system and without having to include deactivating intake valves. Thus, system cost may be reduced. In addition, advancing intake valve timing while exhaust valves are held closed during an engine cycle may reduce an amplitude of intake manifold pressure pulsations. Reducing intake manifold pressure pulsations may reduce engine noise, vibration, and harshness. Further, engine volumetric efficiency may be increased via advancing intake valve timing so that efficiency of active cylinders may be increased while one or more engine cylinders are deactivated.
The present description may provide several advantages. Specifically, the approach may reduce engine noise and vibration. Further, the approach may advance or retard intake valve timing of deactivated cylinders without air flowing through the deactivated cylinders during an engine cycle in response to amplitudes of engine intake manifold pressure pulsations to improve intake valve timing control. Further still, the approach may advance intake valve timing in response to an actual total number of active cylinders while at least one engine cylinder is deactivated to further improve engine operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.